The present invention relates generally to the reclaiming of scrap metal and, more particularly, to an improved process and system for removing contaminating combustibles from the surface of scrap metal wherein the heat content of the contaminating combustibles is recovered.
In the reclamation of scrap metal, particularly scrap aluminum, it is generally desirable to remove contaminants, such as oil, paint, lacquer and grease, etc., from the surface of the metal to be reclaimed. Since it is known that the contaminants have heat content, various processes and equipment have been designed which remove these contaminants and recover their heat content.
U.S. Pat. Nos. 3,839,016 and 3,933,343 to Rawlings disclose a well-type melting furnace for reclaiming metals from metallic scrap material contaminated with combustibles. It includes a large well which is operatively divided into two communicating wells: one being the receiving well for scrap material during melting and the other being the main holding well for molten metal. A combustion chamber, defined over the main holding well, is equipped with a burner secured within the input opening of the combustion chamber to provide the heat for melting and treating the scrap material. Heat from molten material flowing between the holding well and the scrap receiving well produces combustible fumes by vaporizing the combustibles of the scrap material. The heat also preheats the air above the scrap receiving well. A vaporization chamber defined over the scrap receiving well has an exhaust opening and duct means connecting the same with the burner. A blower means secured in the duct means collects the fumes and preheated air from the vaporization chamber for ignition at the burner in the combustion chamber. In this manner, the vaporized combustibles generated by scrap material in the receiving well are prevented from escaping and are utilized in the melting process. Fluxes are also added to the vaporization chamber to prevent oxidation of the scrap.
U.S. Pat. No. 4,319,921 to Pryor et al also discloses a well-type melting furnace divided into two communicating wells: a scrap receiving well and a main holding well. A vaporization chamber is provided over the scrap receiving well for collecting combustible fumes rising from the scrap. To control fume generation and to minimize oxidation of the scrap metal in the receiving well, the receiving well and vaporization chamber are entirely enclosed. The only entry to its interior is through the receiving well doors which are kept closed except during charging and stirring. This thereby enables control over the amount of air admitted to the receiving well which enables control over fume generation and minimizes metal oxidation. As with Rawlings, the process in Pryor recovers the heat content of the fumes by collecting the fumes from the vaporization chamber and incinerating them in the combustion chamber. The fumes are channeled to the combustion chamber from the vaporization chamber by an educator means secured within a circulating passage which connects the respective chambers. A preferred educator means is provided by a burner means which provides preliminary incineration of the fumes prior to their complete incineration in the main well or combustion chamber by the main burner means. While the process disclosed in Pryor may work well for processes wherein the metal is charged in a batch-like manner, the process' requirement of an enclosed side well or vaporization chamber renders it completely unsuitable for continuous charging processes. Moreover, while both of the above processes may work as intended, there is always a need for processes which operate simply and more efficiently.